This is a Q icon. We've made it in iOS style, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 13,300 icons, all in the same style and quality.

Idea of Q Icon by Arriejanne

We've received the idea on October 30, 2012 and created the icons on August 03, 2013

​all the characters of the alphabet

Jeremiah Fischer

I agree. Though, I would like to see these have transparent backgrounds and not just inside a black box like your existing numbers set (which is still cool by the way). Just stand-alone free floating letters would be nice. I have yet to find an icon set that has accomplished this task with great quality. +3 *EDIT: Complete with numbers, symbols, and special chars! :D